Why Copenhagen is building parks that can turn into ponds

Copenhagen's new Enghaveparken will have spaces that can host sporting events during dry weather and fill with water during heavy rains. (COWI, TREDJE NATUR and Platant)

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COPENHAGEN, Denmark — At first glance, the square known as Tåsinge Plads doesn’t look much different from other parks in Copenhagen. A young couple lounges on a small hill surrounded by newly planted trees and wildflowers. Children laugh and play. Old women sit chatting on benches under the shade of tall sculptures shaped like upside-down umbrellas.

But there are hidden features that make Tåsinge Plads part of this seaside city’s plan to survive the effects of climate change.

During heavy rains, the flowerbeds fill with water and wait to drain until the storm runoff subsides. The upside-down umbrellas collect water to be used later to nourish the plantings. And clever landscaping directs stormwater down into large underground water storage tanks. Above those tanks are bouncy floor panels that children love to jump on — when they do, the energy from their feet pumps water through the pipes below.

Just a few years ago, this square was paved with asphalt and dominated by parked cars — a small grassy area was used more as a toilet for dogs than as a park. Now, it’s the cornerstone of a plan to make the surrounding area of Saint Kjelds into what planners here are calling the world’s first “climate-resilient neighborhood.”

The tarmac has been torn up and the greenery reduces the urban-heat island effect. More parks like it are being built to purposefully turn into small ponds during heavy rains, allowing them to capture and retain water on site until the drainage system has capacity to handle it. During the worst deluges, certain streets with raised sidewalks will become “cloudburst boulevards,” creating a Venice-like cityscape of water channeled safely through the city until it can empty into the harbor.

Eventually, Saint Kjelds will be able to withstand — and even welcome — heavy rainfall and flooding. The plan is based on a vision drawn up by Copenhagen-based landscape architects Tredje Natur. Flemming Rafn Thomsen, a founding partner at the firm, says it’s an example of how the job of adapting to climate change can be turned from a seemingly negative thing into a positive one.

“Water is used as a resource to improve urban life,” Rafn Thomsen says. “We look at Copenhagen as a hybrid city where you can fuse nature, urban biology and human beings in a more appropriate balance.”

Handling higher volumes

Copenhagen isn’t alone in re-thinking its relationship with water. Two years ago, Rotterdam unveiled Benthemplein Square, an urban space with three concrete basins that intentionally fill up to store large amounts of water during storms. In the United States, Philadelphia has embarked on a $2.5 billion, 25-year effort to install thousands of rain gardens and permeable surfaces to allow rainwater to seep into the ground rather than run off into sewers and streams.

Copenhagen is advancing on a similarly massive scale. The city has recently been hit by two so-called “100-year flood” events, first in 2011 and then again in 2014. The Intergovernmental Panel on Climate Change predicts that this sort of extreme weather will become increasingly frequent in Denmark, with heavier downpours (as well as more periods of drought). Sea-level rise is a separate but related threat — according to research from the Niels Bohr Institute, the waters around Copenhagen could rise by up to 1.6 meters (more than 5 feet) in the next 100 years.

The flowerbeds of Tåsinge Plads fill with water during heavy rains, while sculptures collect water to nourish plantings. (David Buchmann)

Planning for this future, Copenhagen had to make a choice between two very different paths.

The first option was to expand the city’s existing subterranean sewer and drainage system — its “gray” infrastructure.” This would mean doubling down on the 20th-century notion that the city could handle higher volumes of rainwater as it falls by burying more and larger pipes to handle the runoff.

The second option was more of a “green and blue” system. Rather than funneling all stormwater at once through underground pipes, this option envisioned dealing with water at street level through a network of parks, cloudburst boulevards and retention zones.

Copenhagen opted for a Climate Adaptation Plan that relies mostly on the latter approach. In November, the council unanimously approved plans for 300 surface-based solutions like those in Tåsinge Plads to be implemented over the next 20 years. “The ambition of the Climate Adaptation Plan is to get technical solutions above ground,” says René Sommer Lindsay, manager for project in the neighborhood around Tåsinge Plads. “So when it’s not raining, there is still value in the space.”

One of the highest profile of these projects is the Enghaveparken, a large urban park built in the 1920s. It is to be remade with water at the heart of the design. The park boundary will be marked by a dike that will filter water around the grounds and into 100 small community gardens. More water storage will be provided by excavating below-grade zones where sports such as football and hockey can be played when the park is dry but where water can fill up into retention ponds when it rains. An underground reservoir beneath the park will harvest more rainwater.

Cost considerations

For Copenhagen, the “green and blue” approach was also the most affordable option. It is expected to cost US$1.3 billion — about half the price of more conventional “gray” upgrades. Doing nothing was also an option, but that would only lead to more flood damage, which the city estimated at $2.3 billion over a 100-year period. As Esben Alslund-Lanthén, an analyst at the Danish think tank Sustainia, puts it: “It is both a financially sound investment and one that increases quality of life.”

The upgrades are to be paid for in two primary ways. Any technical adaptations such as below-ground water harvesting or pipe-based infrastructure will be financed through utilities charges. For an average apartment in Copenhagen with a typical amount of water consumption, bills will rise by around 715 kroner (US$100) per year. Meanwhile, elements of these projects related to the urban realm will be backed by the municipal budget. These costs are expected to add up to about US$145 million over 20 years.

While water plays a central role in every one of the improvement projects, community engagement is just as important. When the Tåsinge Plads project began in 2012, more than 10,000 people took part in 170 citizen-led initiatives in the area. By building community gardens and art projects in the previously forlorn space, the community began to shape the square’s future by bringing some meaning to it.

Community engagement is also central to the plans for Enghaveparken, where users are involved in every step of the redevelopment process. For example, locals who enjoy skipping stones across the surface of ponds (there’s a club) helped design a water feature with this activity in mind.

What Copenhagen shows us is that a holistic approach placing citizens at the heart of future-proofing their own city has remarkable payback for society as a whole. These adaptation projects will create 13,000 jobs, while inspiring local ownership of public space, improving quality of life and protecting urban dwellers from the unstoppable forces of climate change. That’s a lot more than you get from burying big new water pipes underground.

“Instead of just having a big concrete hole, we made it into something that has real recreational value,” René Sommer Lindsay says of Tåsinge Plads. “Water isn’t something we need to shield ourselves from.”